Various types of pneumatic pressure regulators are known. For low cost production, typically a major portion of the regulator's housing is formed by a casting which has various machining operations performed thereon. A common type of regulator has a valve seat machined into the casting and a bottom cap to retain the poppet and poppet return spring in the casting in operative relationship with respect to the valve seat. This open bottom design of regulator provides a desirable flow path through the regulator housing, in that the flow path has only a single right angle turn between the valve seat opening and the outlet port. This minimizes the pressure losses on the downstream side of the valve seat. However, machining operations have been required to form the valve seat in the casting as above indicated, threads for the bottom cap, O-ring sealing surfaces, etc. Also, replacement of the valve seat requires replacement of the entire casting, and the regulator requires assembly from two directions, i.e., from the top and bottom.
Also known are closed bottom regulators. In a typical closed bottom regulator, the valve seat is formed by a separate piece inserted into the casting. The valve seat is usually screwed into a threaded hole in the casting after insertion of the poppet and poppet return spring. Although having the advantage of being able to replace the valve seat without having to replace the entire casting, the typical flow path is more complicated on the downstream side of the valve seat and usually involves three right angle turns between the valve seat opening and the outlet port, with pressure losses on the downstream side of the valve seat resulting in lower flow rates when compared to the above mentioned open bottom regulators of comparable size.
Another type of closed bottom regulator was produced by applicants' assignee in the 1960's. In this regulator, the valve seat was provided on a cartridge inserted into a chamber in the main body of the housing and sealed to the main body at confronting planar surfaces by a O-ring disposed in a plane perpendicular to the longitudinal axis of the chamber. The flow path in this regulator was backwards to that of the above mentioned open bottom regulator wherein the valve seat is formed in the casting. However, pressure balancing on the poppet was accomplished at the upstream or high pressure side of the valve seat and the regulator was relatively expensive to manufacture.
It would be advantageous to provide a pneumatic pressure regulator with the main body of the housing formed by a casting that provides a flow path similar to the flow path in open bottom regulators while reducing the amount of machining, as by eliminating the need to machine, for example, a valve seat, threads for a bottom cap, and O-ring sealing surfaces. Moreover, it would be advantageous for such a regulator to have a valve seat that can be replaced without replacement of the entire casting and which enables assembly from one direction only with parts that are self-aligning.
Whether closed bottom or open bottom, pneumatic pressure regulators typically also include a bonnet attached to the main body. The bonnet usually contains a control spring that bears on a piston which closes a control chamber that is connected by an aspirating passage to the regulator's flow passage downstream of the valve seat. As shown in U.S. Pat. No. 3,926,208, the piston may be sealed to an outer wall of the control chamber by an elastomeric V-type packing ring. As further shown in the '208 patent, the piston may have a central relief passage therethrough that is normally closed by the end of a poppet stem. When the downstream or outlet pressure exceeds the set pressure of the regulator, the increased pressure in the control chamber will move the piston against the control spring to permit the poppet valve to close and further to unseat the end of the operator stem from the vent passage, thereby allowing fluid to vent from the control chamber to atmosphere via a side hole in the bonnet.
The use of packing and the like to seal the piston the outer wall of the control chamber introduces hysteresis during forward flow, as does the prior use of flat diaphragms. Too much hysteresis during forward flow is an undesirable characteristic. It would be advantageous to reduce this hysteresis, as by use of a rolling diaphragm to seal the piston. The reduction in hysteresis, however, has been found to allow the diaphragm assembly to vibrate during the pressure venting or relieving mode, usually resulting in a noise which is undesirable. Accordingly, it would be desirable to provide a regulator that has no or low hysteresis during forward flow and no undesirable vibration or noise during the venting mode.